Method of preventing corrosion in pipe-line transportation of refined petroleum oils



Patented Apr. 10, 1951 tmw METHOD OF PREVENTING CORROSION IN I PIPE-LINE TRANSPORTATION OF FINED PETROLEUM OILS Leonard V. Sorg, Richard E. Dickey, and William A. Weaverling, Kansas City, Mo., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application August 21, 1947,

Serial No. 769,990

problem since the development of this method of distributing petroleum products such as kerosene,

Diesel fuel, furnace oils, stove distillate, tractor fuels, and the like. Altho the transportion of crude petroleum usually involves little or no internal corrosion problem, the transportation of refined products has been beset by serious internal corrosion resulting in pitting of the lines and the formation of internal growths or tubercles of rust-like material which seriously impede the fiow of fluids thru the line, partly by restricting the cross-sectional area of the line but more importantly by destroying the streamlined fiow characteristics, resulting in turbulent fiow with high energy losses. A careful study of the phenomenon of corrosion accompanying pipe line transportation of petroleum distillates has indicated that the corrosion is caused by a combination of two principal factors, one being the separation of dissolved water from the oil as a result of temperature reduction, the other factor being the presence of oxygen dissolved in the hydrocarbon as a result of previous contact with the air. Attempts to solve the problem by removal of dissolved water from stocks and by removal of dissolved oxygen have been only partially successful, mainly on account of the special equipment required and expensive operating procedures.

Another method of reducing corrosion has been the introduction into the line of corrosion inhibitors such as sodium nitrite and aqueous sodamid described in U. S. Patents Nos. 2,297,666 and 2,422,515. By this latter method an aqueous solution ofthe inhibitor is injected into the pipe line and the movement of the oil is depended upon to carry the solution thru the line as a separate aqueous phase and bring it into contact with the surfaces of the line where corrosion is occurring. The method sufiers from the disadvantage of requiring considerable time for the inhibitor to be carried thruout the length of the system, and the difficulty of reaching the inside upper surl 2 faces of the line, since the aqueous inhibitor tends to fiow along the bottom of the line. Another difiiculty which has been encountered from the use of aqueous inhibitor solutions results from the extraction of certain substances from the hydrocarbon stocks passing thru the line. For example, when gasoline containing an antioxidant is passed thru the line, a portion of the antioxidant dissolves in the aqueous inhibitor phase which is usually alkaline, then when a batch of water-white kerosene is passed thru the line following the gasoline, a portion of the antioxidant redissolves in the kerosene as a highly colored substance, resulting in discoloration of the kerosene which is objectionable from the standpoint of marketability of this product. A similar difliculty can arise in cases where dyed gasolines are transported where the separate aqueous phase may retain a portion of the dye from the gasoline and introduce it into the kerosene stream later.

We have now discovered a method of preventing internal corrosion of steel pipe lines used for transporting petroleum distillates which entirely avoids the presence of a separate aqueous phase or water layer in the line. Our method is based upon the incorporation into the hydrocarbon of a very small amount of highly effective waterstabilizing agent which completely prevents the separation of water from the stock in the form of a separate aqueous phase or layer. We have found that certain substances are so highly effective that the concentration required has no objectionable effect on the petroleum products being transported, particularly kerosene and furnace oils.

One of the most effective stabilizing agents found for this purpose is the sodium salt of the dioctyl ester of sulfosuccinic acid, the formula of which is NaOSO2C2Ha(CO2CaI-Irz)2. In place of the sodium salt we may use the salts of other alkali metals such as potassium and lithium, or we may use the ammonium salts, the amine salts, particularly the salts of the alkanol amines, such as diethanol and triethanol amines. We may also use the salts of the sulfosuccinic esters with the tetra-alkyl ammonium bases such as tetramethyl ammonium hydroxide. Besides the dioctyl ester, we may use other sulfosuccinic acid esters such as the nonyl ester and any esters of alcohols in the range of about C5 to C12. Mixed esters maybe employed with any of these alcohols and any of the resulting acids may be employed as salts of the bases described hereinabove.

An important requirement of the stabilizing or solubilizing agent employed is that it be soluble water in the hydrocarbon. I having excellent emulsifying characteristics do the hydrocarbon transported, at least to the extent required for stabilization of the dissolved Many substances not meet-this requirement and therefore cannot be employed for our purpose. The substances suitable as moisture stabilizers in our process are .ized by having blfunctional' molecules in which one part associates water. while the. other part associates oil.

A number of substances of this type were tested by dissolving 50 parts per million in gasoline and then'cooling the solution and noting the temperature at which moisture separation became evident by clouding. The following results were obtained:

Tern erature hich Trade Name Manufacturer Moisture Precipitation is Evident, F.

Purified Mahogany A" 5458 I figgf Mamgany '4 Standard on Co. (Ind.) -4 Crude Transformer Soap 52-56 Purified Transformer Soap. 34-38 75 43-4 G-7596H 53-55 Twgegrtie l85-Sorb1tan tri- Atlas Powder oompansk 42-45 Tween8o- Sorbitanmono- 3540 e Triton X-lOO..- 50-53 Triton Rohm dz Haas 00., Inc 54 56 Aerosol 0'1 (Sodium di- American Cyanarnid & 10-15 octyl sulfosuecinic ester). Chem. ,Co. Tret-o-Lite, L,16508 Peroleum Rectii'ying 25-30 a 0. Control (N 0 agent added)- m-es The efiect of the moisture stabilizer in preventing corrosion of steel i shown by the foltransportation of moisture-stabilized products it is important to avoid any accidental introduction of water into the line. This can be accomplished by the use of suitable protective water separators at the, point of charging the line, and by the use of coalescers to separate any entrained water from the stocks entering the line. Drying the line can be accomplished by. various methods suchasby blowing dry air thru the line, by desiccating the gasoline passing thru the line for a period of time until it has dissolved out any water which has collected in the line, or by purging the line with 'a suitable solvent. such as ethyl alcohol which can be passed thru the line ahead of the gasoline. The alcohol, being miscible with water, removes the water and the following stream of gasoline dissolves the alcohol remaining in the line. It is also desirable before drying the line to pass scrapers to remove any accumulated deposits of rust and corrosion in order to restore the line to its maximum efllciency.

Another method of removing water from the line is to pass thru it an oil having a higher concentration of the solubilizer thannormally required for stabilization in a dry line, using for this purpose an oil in which the excess stabilizer is not objectionable. Thus we may use as much as 100 to 500 parts per million of dioctyl sulfolowing experiment, in which clean steel stripswere placed in gasoline containing varied concentrations of the sodium salt of dioctyl sulfosuccinic acid cooled to a temperature of 32 F.

From the above it will be apparent that the dioctyl ester of sodium sulfosuccinic acid is a highly effective moisture stabilizer and prevents.

corrosion down to a concentration of approximately 5 parts per million. Inasmuch as the non-combustible residue from the sulfosuccinate stabilizer is only 14.7% by test, a concentration of '7 parts per million corresponds to approxi-' mately one part per million of added incombustible material which is far below the maxi- -mum concentration which can be tolerated in motor. fuels. In general, we prefer to employ moisture stabilizers which are effective in con- I centrations of not more than about parts per .million, altho somewhat higher concentrations can be used, e. g. 100 to 200 parts per million. If desired, incombustible deposits may be entiresuccinate in an industrial fuel oil distillate to dry the line, after which gasoline can be passed thru the line with only suflicient solubilizer to prevent water separation.

The addition of the moisture stabilizer or solubilizer to the hydrocarbon stock can be made in several ways but most conveniently it can be added to the finished stock at the time of blending with other addition agents or other stocks, for example, in the case of gasoline which is treated with tetraethyl lead, the stabilizer can be added at the same time as the tetraethyl lead and thoroughly mixed with the stock. It is important to add the stabilizer to the stock in the absence of separated water and preferably at a point in the manufacture where the temperature of the stock is at a minimum, usually at atmospheric temperature-commonly 60 to 80 F. insummer and 40 to 60 F. in winter. Thus, in the manufacture of kerosene where the refining operation has heated the kerosene at the time of finishing, it is desirable to withhold the addition of the stabilizer until the kerosene has cooled toatmospheric temperature and deposited all the dissolved water which will separate at that temperature. The stabilizer can then be added while transferring the water-saturated gasoline to a dry shipping tank.

In order to insure that every barrel of stock introduced into the' line is properly stabilized against moisture separation, it is preferred to inject' the stabilizer into all the stocks entering the line in a concentrated solution, for example, a solution in gasoline, kerosene, orother suitable solvent in which it is'more highly soluble such as an alcohol, e. g. ethyl, propyl, or butyl alcohol, or

an aromatic solvent, e. g. benzene, toluene, xylene, cresol, xylenol, etc., or the heavy aromatized distillate from the hydroforming of naphthas comprised largely of methyl naphthalenes. A proportioning pump can be employed to inject the v stabilizer solution at exactly the correct rate to provide the necessary protection to the pipe line with all stocks or with any single stock which may be batched thru the line.

Having thus described our invention what we claim is:

1. The method of preventing corrosion in a ferrous metal conduit carrying hydrocarbon products having a boiling range outside the gasoline boiling range, the steps which consist of reducing the water content below that necessary to saturate the products at the highest temperature encountered in the line but in considerable excess of that necessary to saturate the products at be low about 30 F., and commingling with said hydrocarbon products in the absence of separated water a small amount of an organic solution of an oil-soluble, moisture-stabilizing agent selected from the class consisting of the preferentially oil-soluble alkali metal salts of dioctyl ester of sulfosuccinic acid, the amount of said moisture-stabilizing agent being at least about P. P. M. and sufficient to prevent the formation of a separate water phase when the temperature of said hydrocarbon product is subsequently reduced to below about 30 F., thereby maintaining said conduit free from a separate aqueous phase at temperatures above about 30 F.

2. The method of preventing corrosion in a fer-- rous metal conduit employed for the transportation of petroleum distillate fuels boiling outside the gasoline boiling range, the steps which consist in reducing the water content below that which would saturate the product at the highest temperature encountered in the conduit but in considerable excess of that necessary to saturate the products at the lowest temperature to be encountered in the ferrous metal conduit, and commingling with said fuels as they enter the conduit between about 5 and 200 parts per million of sofined petroleum distillates substantially saturated I with dissolved water but free from suspended or separated water at the prevailing temperature, said method comprising passing through the pipe line an oil having a concentration of between about and 500 parts per million of an alkali metal salt of dioctyl ester of sulfosuccinic acid as a water solutizer to dry the line and subsequently passing a distillate fuel through the line containing a concentration of between about 5 and about 100 parts per million of a moisture-stabilizing agent consisting of an oil-soluble alkali metal salt of dioctyl ester of sulfosuccinic acid, the amount of said stabilizing agent being suflicient to prevent the separation of water from the fuel as a separate liquid phase when the temperature of the pipe line is lowered, and thereby maintaining said pipe line substantially free from a separate aqueous phase which would be conducive to internal corrosion of the pipe line.

LEONARD V. SORG. RICHARD E. DICKEY. WILLIAM A. WEAVERLING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,316,739 Cook Apr. 13, 1943 2,422,515

Anderson June 17, 1947 

1. THE METHOD OF PREVENTING CORROSION IN A FERROUS METAL CONDUIT CARRYING HYDROCARBON PRODUCTS HAVING A BOILING OUTSIDE THE GASOLINE BOILING RANGE, THE STEPS WHICH CONSIST OF REDUCING THE WATER CONTENT BELOW THAT NECESSARY TO SATURATE THE PRODUCTS AT THE HIGHEST TEMPERATURE ENCOUNTERED IN THE LINE BUT IN CONSIDERABLE EXCESS OF THAT NECESSARY TO SATURATE THE PRODUCTS AT BELOW ABOUT 30* F., AND COMMINGLING WITH SAID HYDROCARBON PRODUCTS IN THE ABSENCE OF SEPARATED WATER A SMALL AMOUNT OF AN ORGANIC SOLUTION OF AN OIL-SOLUBLE, MOISTURE-STABILIZING AGENT SELECTED FROM THE CLASS CONSISTING OF THE PREFERENTIALLY OIL-SOLUBLE ALKALI METAL SALTS OF DIOCTYL ESTER OF SULFOSUCCINIC ACID, THE AMOUNT OF SAID MOISTURE-STABILIZING AGENT BEING AT LEAST ABOUT 5 P. P. M. AND SUFFICIENT TO PREVENT THE FORMATION OF A SEPARATE WATER PHASE WHEN THE TEMPERATURE OF SAID HYDROCARBON PRODUCT IS SUBSEQUENTLY REDUCED TO BELOW ABOUT 30* F., THEREBY MAINTAINING SAID CONDUIT FREE FROM A SEPARATE AQUEOUS PHASE AT TEMPERATURES ABOVE ABOUT 30* F. 